1,587 research outputs found
Probing the origin of UX Ori-type variability in the YSO binary CO Ori with VLTI/GRAVITY
The primary star in the young stellar object (YSO) binary CO Ori displays UX
Ori-type variability: irregular, high amplitude optical and near-infrared
photometric fluctuations where flux minima coincide with polarization maxima.
This is attributed to changes in local opacity. In CO Ori A, these variations
exhibit a 12.4 yr cycle. Here, we investigate the physical origin of the
fluctuating opacity and its periodicity using interferometric observations of
CO Ori obtained using VLTI/GRAVITY. Continuum K-band circum-primary and
circum-secondary emission are marginally spatially resolved for the first time
while Br emission is detected in the spectrum of the secondary. We
estimate a spectral type range for CO Ori B of K2-K5 assuming visual
extinction, and a distance of 430 pc. From geometric modelling
of the continuum visibilities, the circum-primary emission is consistent with a
central point source plus a Gaussian component with a full-width-half-maximum
of 2.310.04 milliarcseconds (mas), inclined at 30.22.2 and
with a major axis position angle of 406. This inclination is
lower than that reported for the discs of other UX Ori-type stars, providing a
first indication that the UX Ori phenomena may arise through fluctuations in
circumstellar material exterior to a disc, e.g. in a dusty outflow. An
additional wide, symmetric Gaussian component is required to fit the
visibilities of CO Ori B, signifying a contribution from scattered light.
Finally, closure phases of CO Ori A were used to investigate whether the 12.4
yr periodicity is associated with an undetected third component, as has been
previously suggested. We rule out any additional companions contributing more
than 3.6% to the K-band flux within ~7.3-20 mas of CO Ori A.Comment: 7 pages, 4 figures, accepted for publication in MNRA
Effects of self-directed and other-directed introspection and emotional valence on activation of the rostral prefrontal cortex during aesthetic experience
A K-band spectral mini-survey of Galactic B[e] stars
We present a mini-survey of Galactic B[e] stars mainly undertaken with the
Large Binocular Telescope (LBT). B[e] stars show morphological features with
hydrogen emission lines and an infrared excess, attributed to warm
circumstellar dust. In general, these features are assumed to arise from dense,
non-spherical, disk-forming circumstellar material in which molecules and dust
can condensate. Due to the lack of reliable luminosities, the class of Galactic
B[e] stars contains stars at very different stellar evolutionary phases like
Herbig AeBe, supergiants or planetary nebulae. We took near-infrared long-slit
K-band spectra for a sample of Galactic B[e] stars with the LBT-Luci I.
Prominent spectral features, such as the Brackett gamma line and CO band heads
are identified in the spectra. The analysis shows that the stars can be
characterized as evolved objects. Among others we find one LBV candidate
(MWC314), one supergiant B[e] candidate with 13CO (MWC137) and in two cases
(MWC623 and AS 381) indications for the existence of a late-type binary
companion, complementary to previous studies. For MWC84, IR spectra were taken
at different epochs with LBT-Luci I and the GNIRS spectrograph at the Gemini
North telescope. The new data show the disappearance of the circumstellar CO
emission around this star, previously detectable over decades. Also no signs of
a recent prominent eruption leading to the formation of new CO disk emission
are found during 2010 and 2013.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in MNRAS (in
press
Reduction of finite sampling noise in quantum neural networks
Quantum neural networks (QNNs) use parameterized quantum circuits with
data-dependent inputs and generate outputs through the evaluation of
expectation values. Calculating these expectation values necessitates repeated
circuit evaluations, thus introducing fundamental finite-sampling noise even on
error-free quantum computers. We reduce this noise by introducing the variance
regularization, a technique for reducing the variance of the expectation value
during the quantum model training. This technique requires no additional
circuit evaluations if the QNN is properly constructed. Our empirical findings
demonstrate the reduced variance speeds up the training and lowers the output
noise as well as decreases the number of measurements in the gradient circuit
evaluation. This regularization method is benchmarked on the regression of
multiple functions. We show that in our examples, it lowers the variance by an
order of magnitude on average and leads to a significantly reduced noise level
of the QNN. We finally demonstrate QNN training on a real quantum device and
evaluate the impact of error mitigation. Here, the optimization is practical
only due to the reduced number shots in the gradient evaluation resulting from
the reduced variance.Comment: 11 pages, 10 figure
Gas dynamics in the inner few AU around the Herbig B[e] star MWC297: Indications of a disk wind from kinematic modeling and velocity-resolved interferometric imaging
We present near-infrared AMBER (R = 12, 000) and CRIRES (R = 100, 000)
observations of the Herbig B[e] star MWC297 in the hydrogen Br-gamma-line.
Using the VLTI unit telescopes, we obtained a uv-coverage suitable for aperture
synthesis imaging. We interpret our velocity-resolved images as well as the
derived two-dimensional photocenter displacement vectors, and fit kinematic
models to our visibility and phase data in order to constrain the gas velocity
field on sub-AU scales. The measured continuum visibilities constrain the
orientation of the near-infrared-emitting dust disk, where we determine that
the disk major axis is oriented along a position angle of 99.6 +/- 4.8 degrees.
The near-infrared continuum emission is 3.6 times more compact than the
expected dust-sublimation radius, possibly indicating the presence of highly
refractory dust grains or optically thick gas emission in the inner disk. Our
velocity-resolved channel maps and moment maps reveal the motion of the
Br-gamma-emitting gas in six velocity channels, marking the first time that
kinematic effects in the sub-AU inner regions of a protoplanetary disk could be
directly imaged. We find a rotation-dominated velocity field, where the blue-
and red-shifted emissions are displaced along a position angle of 24 +/- 3
degrees and the approaching part of the disk is offset west of the star. The
visibility drop in the line as well as the strong non-zero phase signals can be
modeled reasonably well assuming a Keplerian velocity field, although this
model is not able to explain the 3 sigma difference that we measure between the
position angle of the line photocenters and the position angle of the dust
disk. We find that the fit can be improved by adding an outflowing component to
the velocity field, as inspired by a magneto-centrifugal disk-wind scenario.Comment: 15 pages, 13 Figure
On the nature of the Herbig B[e] star binary system V921 Scorpii: Geometry and kinematics of the circumprimary disk on sub-AU scales
V921 Scorpii is a close binary system (separation 0.025") showing the
B[e]-phenomenon. The system is surrounded by an enigmatic bipolar nebula, which
might have been shaped by episodic mass-loss events, possibly triggered by
dynamical interactions between the companion and the circumprimary disk (Kraus
et al. 2012a). In this paper, we investigate the spatial structure and
kinematics of the circumprimary disk, with the aim to obtain new insights into
the still strongly debated evolutionary stage. For this purpose, we combine,
for the first time, infrared spectro-interferometry (VLTI/AMBER, R=12,000) and
spectro-astrometry (VLT/CRIRES, R=100,000), which allows us to study the
AU-scale distribution of circumstellar gas and dust with an unprecedented
velocity resolution of 3 km*s^-1. Using a model-independent photocenter
analysis technique, we find that the Br-gamma-line emission rotates in the same
plane as the dust disk. We can reproduce the wavelength-differential
visibilities and phases and the double-peaked line profile using a
Keplerian-rotating disk model. The derived mass of the central star is
5.4+/-0.4 M_sun*(d/1150 pc), which is considerably lower than expected from the
spectral classification, suggesting that V921 Sco might be more distant (d
approx 2kpc) than commonly assumed. Using the geometric information provided by
our Br-gamma spectro-interferometric data and Paschen, Brackett, and Pfund line
decrement measurements in 61 hydrogen recombination line transitions, we derive
the density of the line-emitting gas (N_e=2...6*10^19 m^-3). Given that our
measurements can be reproduced with a Keplerian velocity field without
outflowing velocity component and the non-detection of age-indicating
spectroscopic diagnostics, our study provides new evidence for the
pre-main-sequence nature of V921 Sco.Comment: 17 pages, 11 figures, 3 tables, accepted by Ap
Effects of self-directed and other-directed introspection and emotional valence on activation of the rostral prefrontal cortex during aesthetic experience
The medial area of the rostral prefrontal cortex (rPFC) has been implicated in self-relevant processing, autobiographical memory and emotional processing, including the processing of pleasure during aesthetic experiences. The goal of this study was to investigate changes in rPFC activity using functional near-infrared spectroscopy (fNIRS) in response to affective stimuli viewed in a self-relevant or other-relevant context. Positive and negative images were displayed to 20 participants under two viewing conditions where participants were asked to think of their own emotions (self) or think about the emotions of the artist who created the work (other). The results revealed an increase of HbO when participants viewed images during the other-condition compared to the self-condition. It was concluded that viewing stimuli from the perspective of another was associated with an increase of cognitive demand. The analysis of deoxygenated haemoglobin (HHb) at right hemispheric areas revealed that activation of the rPFC during the other-condition was specific to the negative images. When images were viewed from the perspective of the self, activation of the rPFC significantly increased at the right-medial area of the rPFC for positive images. Our findings indicate that the influence of valence on rPFC activation during aesthetic experience is contingent on the context of the viewing experience and there is a bias towards positive emotion when images are viewed from the context of the self
Monte-Carlo radiative transfer simulation of the circumstellar disk of the Herbig Ae star HD 144432
Studies of pre-transitional disks, with a gap region between the inner
infrared-emitting region and the outer disk, are important to improving our
understanding of disk evolution and planet formation. Previous infrared
interferometric observations have shown hints of a gap region in the
protoplanetary disk around the Herbig Ae star HD~144432. We study the dust
distribution around this star with two-dimensional radiative transfer modeling.
We compare the model predictions obtained via the Monte-Carlo radiative
transfer code RADMC-3D with infrared interferometric observations and the
{\SED} of HD~144432. The best-fit model that we found consists of an inner
optically thin component at 0.21\enDash0.32~\AU and an optically thick outer
disk at 1.4\enDash10~\AU. We also found an alternative model in which the
inner sub-AU region consists of an optically thin and an optically thick
component. Our modeling suggests an optically thin component exists in the
inner sub-AU region, although an optically thick component may coexist in the
same region. Our modeling also suggests a gap-like discontinuity in the disk of
HD~144432.Comment: 18 pages, 12 figure
Evidence of a discontinuous disk structure around the Herbig Ae star HD 139 614
A new class of pre-main sequence objects has been recently identified as
pre-transitional disks. They present near-infrared excess coupled to a flux
deficit at about 10 microns and a rising mid-infrared and far-infrared
spectrum. These features suggest a disk structure with inner and outer dust
components, separated by a dust-depleted region (or gap). We here report on the
first interferometric observations of the disk around the Herbig Ae star HD
139614. Its infrared spectrum suggests a flared disk, and presents
pre-transitional features,namely a substantial near-infrared excess accompanied
by a dip around 6 microns and a rising mid-infrared part. In this framework, we
performed a study of the spectral energy distribution (SED) and the
mid-infrared VLTI/MIDI interferometric data to constrain thespatial structure
of the inner dust disk region and assess its possibly multi-component
structure. We based our work on a temperature-gradient disk model that includes
dust opacity. While we could not reproduce the SED and interferometric
visibilities with a one-component disk, a better agreement was obtained with a
two-component disk model composed of an optically thin inner disk extending
from 0.22 to 2.3 au, a gap, and an outer temperature-gradient disk starting at
5.6 au. Therefore, our modeling favors an extended and optically thin inner
dust component and in principle rules out the possibility that the
near-infrared excess originates only from a spatially confined region.
Moreover, the outer disk is characterized by a very steep temperature profile
and a temperature higher than 300 K at its inner edge. This suggests the
existence of a warm component corresponding to a scenario where the inner edge
of the outer disk is directly illuminated by the central star. This is an
expected consequence of the presence of a gap, thus indicative of a
pre-transitional structure.Comment: 14 pages, 6 figure
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